Diffusing lens for spotlights with axially oriented filaments



July 11, 1967 F. M. NEAL 3,330,951

DIFFUSING LENS FOR SPOTLIGHTS WITH AXIALLY ORIENTED FILAMENTS Filed May 17, 1965 2 Sheets-Sheet INVENTOR. Frank/in M. Neal AGE/VT July 11, 1967 F. M. NEAL 3,330,951

DIFFUSING LENS FQR SPOTLIGHTS WITH AXIALLY ORIENTED FILAMENTS Filed May 17, 1965 2 Sheets-$heet 2 Hil 60 lg e2 .L M g1 64 E INVENTOR. Frank/in M. Neal BY r dude. 111 M AGENT United States Patent 3 331L951 DIFFUSING LENS i on srorrronrs wrrn AXIALLY ORENTED FHANENTS Franklin M. Neal, Corning, N.Y., assignor to Corning Glass Works, Corning, N.Y., a corporation of New York Filed May 17, 1965, Ser. No. 456,277 8 Claims. (Cl. 240106) ABSTRACT OF DISCLOSURE This invention relates to diffusing lenses and more particularly to a diflusing lens for use in combination with a spotlight device comprising a reflector in the form of a surface of revolution about an axis and an incandescent filament elongated along that axis.

When a long incandescent filament is located along the axis of a reflector in a spotlight, the images of the filament produced on a surface in front of the spotlight are oriented radially with respect to the axis of the reflector. When the device is focused to provide a small spot of light, the images intersect one another at the reflector axis, and when the lamp is focused for the smallest possible light spot, the images intersect one another at approximately their midpoints. The intersection of such images results in a spot of light which has a higher intensity near its center, where the images intersect, than at its outer edges.

This nonuniformity can be corrected to some degree by a diffusing lens comprising a plurality of diffusing flutes extending in radial directions with respect to the reflector axis and curved in transverse cross section. Due to the transverse curvature of the flutes, the refracting power of each flute varies along its width, such that light rays passing through the flute at various transverse locations are refracted differentially, thereby producing image diffusion. In order for the net effect of the flutes to be uniformthroughout the lens, it is necessary that the average transverse diffusing ability of the flutes be substantially uniform at varying distances from the center of the lens. Since the diffusing ability of a flute is a function of the range of refracting powers exhibited by the flute at varying transverse locations, uniform diffusion may be accomplished by means of flutes which are in the form of arcs of circles in cross section and which vary in radius from a minimum near the center of the lens to a maximum at the periphery thereof, the refracting power of a flute along the edge thereof being substantially constant. Although such flutes provide satisfactory diffusion, it is extremely diflicult to manufacture lenses having flutes which vary in radius along their lengths. On the other hand, although flutes of uniform radius along their lengths are practical to manufacture, the variation in width of flutes of uniform radius causes longitudinal variation in the diflusing ability of such flutes. Accordingly, if advantage is to be taken of the ease of manufacture of lenses having radial flutes with uniform radii of curvature along their lengths, it is necessary to provide means for maintaining the average diffusing ability of 3,330,951 Patented July 11, 1967 the total number of flutes substantially constant, regardless of variations in the individual flutes.

Therefore, it is an object of the present invention to provide a diffusing lens comprising a plurality of radially extending flutes having surfaces each of which may have a constant transverse radius of curvature, while at the same time providing a lens the average diffusing ability of which is uniform at varying distances from the center thereof.

This object is accomplished, according to one embodiment of the invention, by the provision of a diffusing lens comprising a plurality of radially extending flutes, the flutes being arranged in pairs, the flutes having transverse curvatures such that two flute edges in each pair define locations of maximum refracting power of-a flute, while the two remaining flute edges in the same pair define locations of minimum refracting power of a flute.

The invention will be described in detail with reference to the accompanying drawing, in which:

FIGURE 1 is a plan view of a diffusing lens according to the invention,

FIGURE 2 is a view taken on line 22 of FIGURE 1,

FIGURE 2a is a sectional view taken on line 2a2a of FIGURE 1, and

FIGURES 3 5 are sectional views similar to that of FIGURE 2 illustrating alternative flute configurations,

FIGURE 6 is a view of a spotlight having an axially oriented light-producing filament with a lens incorporated therein.

Referring to FIGURES 1 and 2, glass diffusing lens 10 comprises a plurality of diffusing flutes, such as 12 and 14. As illustrated in FIGURE 2, flutes 12 and 14 have transverse curvatures in the form of arcs of circles, i.e., the surfaces of the flutes are in the form of portions of cylinders having their axes oriented generally in a radial direction with respect to the lens center 16. The surfaces of flutes 12 are concave, while those of flutes 14 are convex. The semicylindrical surfaces have substantially equal radii of curvature. As can be seen from FIG- URE 1, flutes 12 and 14 become progressively narrower in the direction of the center 16 of the lens. The lens is designed such that the narrowing of the flutes toward the center of the lens is accomplished by progressively narrowing the cylindrical surfaces of the flutes, while maintaining the curvatures thereof constant.

The paths of representative light rays passing through flutes 12 and 14 are illustrated in FIGURE 2. The light rays have been substantially collimated by a reflector, such as reflector 60 of FIGURE 6, and fall upon plane .surface 26 of lens 11 substantially normal thereto. The

cylindrical surfaces of flutes 12 are oriented such that at the maximum width of a flute and at the intersections of the flute with the adjoining flutes 14, each flute 12 has substantially a zero refracting power, such that light rays A and F pass therethrough as indicated without refraction. The refracting power of flute 12 gradually increases to a maximum at its vertex, where the angle between the surfaces of the flute and light rays such as C and D imparts maximum refraction to the light rays. At intermediate locations on the surfaces, light rays, such as B and E are refracted to a lesser degree. The light rays after passing through flute 12 cross in front of the lens and subsequently diverge, thereby producing diffusion of light passing through the flute.

Since flute 14 is convex, its maximum refracting power is in the vicinity of its edges, as illustrated by the maximum refraction imparted to rays G and L. Flute 14 has zero refracting power at its center, through which ray J passes without refraction, while the flute has intermediate refracting powers elsewhere, as indicated by the refraction imparted to rays H and K.

As the surfaces of the respective flutes 12 and 14 are narrowed, it will be seen that the surface areas which are removed from flutes 12 are the areas of minimum refraction, while those removed from flutes 14 are the areas of maximum refraction. This phenomenon is illustrated in FIGURE 2a, which is a sectional view of the flutes of FIGURE 2, taken intermediate their ends. The narrowing of the flutes leaves only the peaks of flutes 12, which are the portions which impart maximum spread to transmitted light, while the narrowing of prisms 14 leaves the portions imparting minimum spread. Thus, there is a tendency for the total light distribution of the lens to remain substantially uniform at varying distances from center 16. If all flutes were of the same type, for example, flutes similar to flutes 14, light passing through the ends of the flutes nearer the center of the lens would tend to be concentrated near the center of the spot of illumination, due to the absence of the areas of maximum refraction from each of the flutes. Similarly, if each flute were similar to flutes 12, the ends of the flutes nearer the center of the lens would tend to illuminate the outer portions of the spot of light more intensely than the center thereof, due to the absence of the areas of minimum refraction from the ends of the flutes nearer the center.

As can be seen from FIGURE 1, lens comprises flutes divided into three series of concentric bands. The 'outer band comprising flutes 12 and 14 extends from the periphery of the lens to approximately midway between the periphery and center 16. Between the inner ends of the outer band of prisms and the center of the lens are two bands of equal widths, comprising respectively flutes 18 and 20 and flutes 22 and 24. Flutes 18 and 22 are identical in transverse curvature with flutes 12, while flutes 20 and 24 are identical in transverse curvature with flutes 14. Although a lens could be made with flutes 12 and 14 extending from the periphery to the center 16, the width of the respective flutes would be extremely small near the center of the lens, approaching zero at the center, and the manufacture of lenses of such minute detail is extemely difiicult. For this reason, the flutes are divided into the respective bands, with the width of the ends of the flutes at the outer edges of the respective bands being equal. Although the inner ends of the flutes of the inner band of the present lens approach zero in width, the radial interval along which the flute width is small is substantially less than the corresponding intervals for a lens having only a single band of flutes extending along the entire radius of the lens.

Flute configurations satisfying the requirements for increased uniformity of light distribtution in spot may vary from the configurations illustrated in FIGURES 1 and 2. For example, the configuration illustrated in FIGURE 3 comprises a repetitive pattern of paired flutes 30 and 32 having their maximum refractive powers along the outer edges of the pair and zero refractive power along the joined edges of the pair. The configuration illustrated in FIGURE 4 comprises paired flutes 40 and 42, identical with flutes 30 and 32 and paired flutes 44 and 46 having their maximum refractive powers at the joined edges of the pair and their areas of zero refractive power at the outer edges of the pair. A further variation is illustrated in FIGURE 5, wherein uniformity of light distribution in an illuminated spot is accomplished by means of a repetitive pattern of paired flutes 50 and 52. It will be observed that flutes 52 are negative flutes, i.e., they are formed as depressions in the transparent material, rather than projections thereon.

The incorporation of a lens according to the present invention in a spotlight having an axially oriented lightproducing filament is illustrated in FIGURE 6. The device comprises a reflector 60 having an inner reflecting surface 61 in the form of a paraboloid of revolution about axis 62. Light source 64 has a filament 66 which is elongated along axis 62. Diffusing lens 10 is oriented substantially perpendicular to axis 62, with its center 16 on axis 62.

4 Lens 10 has been illustrated as having one plane surface and one surface having thereon the radially extending diffusion flutes of the invention. It will be appreciated that if an additional pattern is intended to be superimposed upon the diflused light pattern provided by the flutes of the invention, plane surface 26 may be provided with flutes or prisms of any desired configuration. Lens 10 may be incorporated in the lighting device with the flute configuration of the invention applied to either the inner or outer surface thereof.

Although the invention has been described as embodied in a substantially flat lens, it will be appreciated that the flutes of the invention may be applied to either concave or convex lens or refractor surfaces. In such cases, the transverse curvatures of the flutes will remain substan tially the same as illustrated, with only minor modifications to adapt them to the basic curved surface, such modifications being easily made by those skilled in the art.

The present invention has been exemplified by certain flute configurations illustrated and described above. It will be appreciated that other flute arrangements may be provided within the spirit of the invention, and, accordingly, it is intended that the scope of the invention be limited only by the scope of the appended claims.

I claim: 1. A lens comprising a transparent body having a plurality of first light-diffusing flutes and a plurality of second light-diffusing flutes extending in generally radial directions with respect to a common center,

each said flute being curved in transverse cross-section so as to spread light beams passing therethrough,

said first flutes having refracting powers which vary transversely across the width of said flutes from maximum in the vicinity of the edges thereof to minimum at generally central locations intermediate said edges,

said second flutes having refracting powers which vary transversely across the width thereof from minimum in the vicinity of the edges thereof to maximum at a central location intermediate said edges,

said maximum refracting powers of said first flutes decreasing in the direction of said common center, and said minimum refracting powers of said second flutes increasing in the direction of said common center.

2. A lens according to claim 1 in which each said flute has a surface which is in the form of a portion of a circle in transverse cross-section.

3. A combination of a lens according to claim 1 with:

a reflector having a reflecting surface in the form of a surface of revolution about an axis, and

a light source located between said reflecting surface and said lens and comprising a filament elongated along said axis,

said common center being substantially on said axis.

4. A lens according to claim 1 in which said first and and second flutes are arranged in pairs, each said pair comprising one said first flute and one said second flute.

5. A lens according to claim 1 in which each said first flute has a minimum retracting power of zero.

6. A lens comprising a transparent body having thereon a plurality of light-diffusing flutes extending radially with respect to a common center,

each said flute being curved in transverse cross-section so as to spread light beams passing therethrough, said flutes being in adjacent pairs, said pairs being identical to one another,

said flutes of each said pair including four radially extending flute edges,

two said flute edges of each said pair being at locations of maximum refracting power of a flute at each location along the length thereof, and

two said flute edges of each said pair being at locations of zero retracting power of a flute at the outer radial extremity thereof and being at locations of minimum refracting power thereof at the remaining locations along the length thereof,

one said flute of each pair comprising a convex surface in the form of a portion of a circular cylinder, and

the other said flute of each pair comprising two concave surfaces in the form of portions of circular cylinders.

7. The combination of a lens according to claim 6 with:

a reflector having a reflecting surface in the form of a surface of revolution about an axis, and

a light source located between said lens and said refiecting surface and comprising a filament elongated along said axis,

said common center being on said axis.

8. The combination according to claim 7 in which said lens is a substantially transparent body extending substantially perpendicular to said axis.

References Cited UNITED STATES PATENTS 2,508,063 5/1950 Gross 240M125 X 2,877,342 3/1959 Beach 24041.4

FOREIGN PATENTS 539,932 4/1957 Canada.

NORTON ANSHER, Primary Examiner.

5 W. M. FRYE, Assistant Examiner. 

1. A LENS COMPRISING A TRANSPARENT BODY HAVING A PLURALITY OF FIRST LIGHT-DIFFUSING FLUTES AND A PLURALITY OF SECOND LIGHT-DIFFUSING FLUTES EXTENDING IN GENERALLY RADIAL DIRECTIONS WITH RESPECT TO A COMMON CONTER, EACH SAID FLUTE BEING CURVED IN TRANSVERSE CROSS-SECTION SO AS TO SPREAD LIGHT BEAMS PASSING THERETHROUGH, SAID FIRST FLUTES HAVING REFRACTING POWERS WHICH VARY TRANSVERSELY ACROSS THE WIDTH OF SAID FLUTES FROM MAXIMUM IN THE VICINITY OF THE EDGES THEREOF TO MINIMUM AT GENERALLY CENTRAL LOCATIONS INTERMEDIATE SAID EDGES, SAID SECOND FLUTES HAVING REFRACTING POWERS WHICH VARY TRANSVERSELY ACROSS THE WIDTH THEREOF FROM MINIMUM IN THE VICINITY OF THE EDGES THEREOF TO MAXIMUM AT A CENTRAL LOCATION INTERMEDIATE SAID EDGES, SAID MAXIMUM REFRACTING POWERS OF SAID FIRST FLUTES DECREASING IN THE DIRECTION OF SAID COMMON CENTER, AND SAID MINIMUM REFRACTING POWERS OF SAID SECOND FLUTES INCREASING IN THE DIRECTION OF SAID COMMON CENTER. 